For more than 25 years, there have been two basic types of plastic lids for large commercial and industrial (1 cubic yd.-16 cubic yd.) solid waste containers. They have been either, a single sheet of plastic formed with various rib configurations, or a hollow double wall fabrication with an even greater variety of ribbing combined with partial fusion of the top and bottom walls. Each type has significant advantages as well as known drawbacks.
Single Wall Lid Advantages:
Both types of lids are limited to a maximum weight of approximately 15 pounds for lifting ease. Therefore, the double wall type has approximately half the wall thickness of its single wall counterpart. In the highly abusive environment of the solid waste industry, the thicker single wall lids last longer due to the simple fact that it is inherently more cut, puncture and abrasion resistant. The thicker wall also resists UV degradation far longer. Double wall lids will also allow the ingress of rainwater when punctured. This may result in an unwanted shower for the user when the lid is rotated open or closed. In winter conditions when the water is frozen to ice, the lids can become too heavy for the user to lift. Single wall lids do not retain water except in the open horizontal position and are easily emptied in a controlled fashion.
For any given rib height, the single wall additional thickness increases the load bearing of the rib by the cube of the increase in the thickness (i.e. if you double the thickness of the rib wall, the stiffness is increased 8 times). Load bearing is important for safety; primarily with regard to children playing on top of a container. Additionally, load bearing is required to resist collapse of the lid into the container due to excessive snow loads or trash bags piled on top of the lids.
The delivery and storage costs of single wall lids are nearly half the cost of double wall lids. Single wall lids rest one on the other every vertical one-half inch. The typical double wall lid has a vertical nesting depth of nearly two inches per lid. A full truckload of double wall lids weights about 23,000 lbs. (1560 lids) whereas a full truckload of single wall lids weighs about 40,000 lbs. (2700 lids). The same issues affect the amount of storage space required throughout the distribution process.
Double Wall Lid Advantages
The double wall lid is superior to the single wall lid with regard to usability, i.e., the person opening the lid to deposit trash prefer the double wall type because it will not twist laterally when lifted off center as is the case with single wall lids. Standing to one side and lifting off center is necessary when depositing larger articles or trash bags as the typical lid in a pair will only provide an opening which is 30 inches to 36 inches wide.
This lateral twisting is a problem for the user because the side of the lid opposite that which is raised with one hand will not lift to the same height as the other (typically 12 or more inches lower) and will effectively block the deposit of trash with the users other hand. This is not a mere annoyance, because in most cases and especially on larger containers, the user will throw open the lid over the back of the container and leave it in the open position due to the difficulty of retrieving the lid and closing it. In communities where they are used, it is not uncommon to find the majority of large waste containers with the lids left open. This condition is obviously unsightly and creates a real health and litter problem in any community.
The double wall lid has significantly stronger hinge lugs than single wall lid fabrications. This is especially true of rotationally molded double wall lids. Most single wall fabricating techniques stretch the material thinner in all raised areas such as ribs and hinge lugs. Furthermore, the hole for the hinge rod is drilled through the thinner stretched wall. This 9/16 inches to 11/16 inches diameter hole is by necessity ½ inc ⅝ inches from the edge of the plastic fabricated sheet. When stressed, the ½ inch diameter hinge rod can pull through the edge with relative ease.
The double wall hinge hole for the lid pivot shaft extends through the side of a boxed hinge lug that has no nearby edge to pull through. This type of fabrication requires the hinge rod to be pulled through the entire side and back wall of the boxed lug in order to fail. Even with double wall fabrications that stretch the wall material thinner as in typical single wall fabrication, the double wall boxed lug is far stronger and will hold the lid on the container far longer than is the case for single wall lids.